Large wheels create better traction?

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5thGenRR

New Member
When you say that it had much larger wheels compared to the others was this a new(er) unit in a consist with older ones? As a comparison SD40's have 40" and 90MAC's have 44" wheels. There are experiments with even larger wheels I believe 45" and that is on the ES4400's. We have done a couple retrofits on them now. I don't work the drop table so I don't have any more info on the 45"ers.

As far as the larger wheels go the higher the tractive effort they get the bigger the wheels have grown. So that may be a partial answer for you.
 

stlgevo51

Steam Chaser
Steam engines are definitely opposite. The smaller the driver size, the better tractive effort and traction the locomotive will produce. That's why switchers and low speed pullers have the smallest wheels.
 

Robert Gift

former OL presenter
Wish I knew more. I only saw a picture.
It had significantly larger wheels.

Yes, the steam locomotive compromises speed with tractiveffort.

Larger diameter = greater speed but lower moment arm.
 

Kevin M

New Member
Im going out on a limb here but newwer engines have bigger traction moters. Larger wheels may be needed to fit the traction moter as they take up more space.
Kevin
 

5thGenRR

New Member
Kevin,
Weather the limb be big or small you may be on to something. If I can, tomorrow ill go out to our wheel garden and do some measuring.
 

kenw

5th Generation Texian
Steam engines are definitely opposite. The smaller the driver size, the better tractive effort and traction the locomotive will produce. That's why switchers and low speed pullers have the smallest wheels.
smaller wheels mean you can have more of them, and more smaller wheels simply have that many more places to touch the rails. The biggest and smallest wheels each only touch the rail in one single small spot. More wheels means more spots.
 

5thGenRR

New Member
I haven't really done any diggin on theory but here is what I found when I surveyed wheel sizes:
GE
40": -8 & -9's
42": C44AC & C45 (ES4400)

EMD
40": GP38, GP39, GP40, SD40 & SD60
42": 70M & 70ACE
44": SD90

I know there are some models I forgot but I needed road numbers to look them up and I was using numbers out of my head.
 

Robert Gift

former OL presenter
I haven't really done any diggin on theory but here is what I found when I surveyed wheel sizes.


I know there are some models I forgot but I needed road numbers to look them up and I was using numbers out of my head.
The wheels on the foreign locomotive appeared much bigger than typical. I assume much larger than 44-inches. Maybe I am wrong.
 
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5thGenRR

New Member
The wheels on the foreign locomotive appeared much bigger than typical. I assume much larger then 44-inches.
They shouldn't be or shouldn't have been. I did talk to a few old timers after I sent my last message to ask what the deal is with gear ratios and wheel sizes. Apparently EMD has many gear ratios. One of the common sizes is 62:15. An old timer who is long retired once told me that was about the same as 4.11's on a truck/car. The one fella has experience with industries' locomotives as well as rail roads. He said that some of the Mill's/Mine’s/Scrap Yards and the like use different ratios or smaller wheels than the ones I listed in a previous post. He said what they want to do is use 1 unit to pull say 20 cars. So they’re geared low or have small wheels. The locomotives will take off fast and appear to have a lot of power but because of that they will not go very fast. I guess it isn't uncommon for them to have a max speed of 30MPH. Even in this configuration the tractive effort is real good. As far as the "bigger" wheels there was a theory that they wore less and it would save money in the long run. I guess that's not necessarily true in the real world. They also said you will most likely only see 40-42" wheels so that the units are compatible with each other. Otherwise there will be instant wheel slip issues.
 

Triplex

New Member
smaller wheels mean you can have more of them, and more smaller wheels simply have that many more places to touch the rails. The biggest and smallest wheels each only touch the rail in one single small spot. More wheels means more spots.
Not a good description. Number of wheels is determined by axle load (how many wheels it takes to spread the locomotive's weight) and tractive effort/adhesion limits (a higher tractive effort locomotive needs more weight on drivers to not slip). The formula for steam tractive effort depends on cylinder dimensions, steam pressure and driver diameter. The number of axles doesn't figure into it. A larger wheel is like a long lever arm: it allows the end (the wheel rim) to turn faster but with less force.

To the original poster:
Do you remember where the locomotive was from? Any other details about it? Specifically, was it a very old rather than new locomotive? Many old electrics had large wheels; there weren't many diesels made in that era, but I can think of one or two.
 

kenw

5th Generation Texian
Not a good description. .
i wasn't going to give an engineering description of the physics here, but if the weight is the same (which was my basis), my point remains. It's a railfan discussion, not an engineering board.
 

Robert Gift

former OL presenter
... Do you remember where the locomotive was from? Any other details about it? Specifically, was it a very old rather than new locomotive? Many old electrics had large wheels; there weren't many diesels made in that era, but I can think of one or two.
I may have seen it in my Facebook page and was not able to copy it and paste it. It may have been in Indonesia in Indonesian language. Maybe it was electric but I would have thoughthat I would have noticed electric or diesel.

So, on a steam locomotive, you wanto place as little weight on the pilot and trailing wheels so more weight is on the drivers?

So what is tractiveffort on a diesel where all wheels are powered. 1 ?
Thank you.
 




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